The present invention relates to a photosensitive material suitable for protective films (e.g. the surface coating films of semiconductor devices), the interlaminar insulating films of thin-film multilayer circuit boards, etc. It relates to, in particular, heat-resistant polyimides, precursors thereof, photosensitive polyimide precursor compositions containing the precursors, and negative-working photosensitive materials developable with an alkaline aqueous solution which contain the precursors, and a process for forming a resin pattern.
As photosensitive heat-resistant materials for obtaining heat-resistant polymers, there have been known the materials disclosed in JP-B 5-67026, i.e., the materials obtained by reacting an aromatic tetracarboxylic acid dianhydride with an olefin unsaturated alcohol to synthesize an olefin aromatic tetracarboxylic acid diester, and polymerizing this compound and a diamine by dehydrating condensation using a carbodiimide, to introduce thereinto a photosensitive group through a covalent bond; and the materials disclosed in JP-B 63-31939, i.e., the materials obtained by reacting an aromatic tetracarboxylic acid dianhydride with an aromatic diamine to obtain a poly(amic acid), and reacting this compound with an amine compound having a photosensitive group, to introduce the photosensitive group thereinto through an ionic bond.
In both of these prior art references, a negative relief pattern is obtained by applying a varnish prepared by dissolving the photosensitive heat-resistant material in a suitable organic solvent on a substrate, drying the varnish to form a coating film, irradiating the film with ultraviolet light through a suitable photomask to light-cure the exposed portion, and developing and rinsing the film with organic solvents, respectively.
However, when an organic solvent is used as a developer in pattern formation, exposed portion tends to be swollen during development, so that a pattern is difficult to obtain with high resolution. Moreover, the employment of an organic solvent involves problems such as undesirable influences on the health of workers, much labor required for treating a waste fluid, etc.
For solving such problems, for example, positive-working polymers obtained by introducing naphthoquinonediazidosulfonylamide groups into the carboxyl groups of a poly(amic acid) have been proposed as materials developable with an aqueous liquid (JP-A 6-258835). Since the naphthoquinonediazidosulfonylamide groups are converted to carboxyl groups by light irradiation, these polymers are characterized in that the exposed portion becomes soluble in an alkaline queous solution. Therefore, they are used as positive-working photosensitive materials.
The above-mentioned positive-working photosensitive materials, however, are disadvantageous in that a long time is required for development and that the sensitivity is not sufficient at a large film thickness (10 .mu.m or more).